Stringed musical instruments are generally provided with tuning means for adjusting the tension of their strings to a desired level, typically, by slightly varying the tension of the strings or adjusting the distance between the bridges which support the strings at their ends. Some of the stringed musical instruments, such as electric guitars, are additionally provided with vibrato means for varying the tension of the strings during performance without upsetting the tuned state of the strings to produce vibrato effects.
FIGS. 1 through 4 of the appended drawings illustrate a conventional electric guitar and a tremolo or vibrato assembly 3 provided therein. These and other drawings appended to this application illustrate the guitar as it is placed flatly on a flat surface or as seen by the player of the guitar. Therefore, a guitar which is being played will be seen inverted from the illustrated attitude to a beholder standing in front of the guitar.
A set 2 of strings 2a, 2b, 2c, 2d, 2e and 2f are anchored at opposite ends 3 and 4 of a guitar body 1 by the vibrato assembly 3 and a tension adjusting assembly 5, respectively. The strings 2 can be tuned by turning the corresponding knobs 5a. The tension of the strings 2 can be varied also by rocking a lever arm 6 provided in the vibrato assembly 3 during performance.
The vibrato assembly 3 is now described in detail with reference to FIGS. 2 through 4. One end of each of the strings 2 is passed through a bridge 9 having a rectangular annular shape. These bridges 9 are movably mounted on a bridge base plate 7 or string support member so as to be adjustable of their heights with respect to the major surface of the guitar body 1 and of their positions along the lengthwise direction of the strings 2. The strings 2 are each further passed through a weight 8 which is fixedly secured to the bridge base plate 7 and are each fixed to the free end of the weight 8 which is received in a common cavity of the guitar body 1. The bridge base plate 7 is hinged to the guitar body 1 by way of screw heads 10 so as to be able to move away from and toward the guitar body 1. The free end of the weight 8 is coupled to internal parts of the cavity in the guitar body 1 by way of tension coil springs 11 so that the bridge base plate 7 is urged toward the guitar body 1 against the tension of the strings 2 as shown in FIG. 3. The lever arm of the handle bar 6 is fixedly attached to the bridge base plate 7 and extends towards the tension adjusting assembly 5, passing the screw heads 10 on which the base plate 7 is hinged.
When the handle bar 6 is pressed towards the guitar body 1, the bridge base plate 7 is swung away from the guitar body 1 against the tension of the tension coil springs 11, thereby slightly moving the bridges 9 towards the tension adjusting assembly 5 and slightly reducing the tension of the strings 2 as shown in FIG. 4. A vibrato effect can be produced by repeatedly alternating these tensioned and loosened conditions of the strings 2 at a desired rate and stroke. In this conventional vibrato assembly, since all of the strings 2 are anchored under tension to the bridges 9 which are secured to a common moveable bridge base plate 7, moving the bridge base plate 7 with the handle bar 6 causes the tension of all the strings 2 to vary only in unison and by a same degree.
Further, since all of the strings 2 are anchored under tension to a common moveable bridge base plate 7, when one of the strings is cut off during performance, the bridge base plate 7 is slightly displaced because the tension it receives from the strings is reduced by the contribution of the cut string to the total tension before it is cut off, the remaining strings are brought slightly out of tune and the player may find it difficult to continue his performance with the remaining strings.
After the broken string is replaced with a new one, all of the strings have to be tuned again and this process takes a long period of time because not only the new string but also the remaining strings are required to be tuned.
Meanwhile, there have recently arisen demands for guitars capable of effecting a wide range of adjustment of string tension for a freer, more sophisticated, and novel playing effects.